The present invention relates to a process and installation for the reduction of iron minerals.
Numerous processes are known for obtaining the reduction of iron minerals.
A comparison of the respective interests of these different processes, is taken purely from the industrial point of view which is normally the only consideration, turns on the costs of preparing the reduced minerals.
From this point of view, the process of reduction in accordance with the present invention, as will appear from the following description, is most advantageous because it has a very high energy yield; it utilizes as the reducing agent reducing gases generated entirely or in part by the furnace itself from cheap material; and it provides, in certain embodiments of the process as a by-product of the reduced mineral, useful materials whose value improves the cost of the reduction operation.
The process in accordance with the present invention carries out the reduction using CO or a mixture of CO and hydrogen.
The laws regulating the chemical equilibrium are known when such reducing gases are mixed with the iron mineral at high temperature.
The reducing power of the gases is defined by the following expression: ##EQU1## in which, for example, (H.sub.2) is the number of molecules of hydrogen per unit of volume. Further, it is known that to be able to reduce the minerals to iron at a temperature on the order of 1000.degree. C., the reducing power of the gases should be greater than 70%.
The assignee of the present invention and application has commercialized for a long time a type of shaft furnace called "FOUR ERIM" as disclosed in French Patent No. 885,257. Such a furnace will be considered hereinafter with respect to the discussion of the present invention.
This furnace has an exterior shell provided at its upper part with charging apparatus for carbon, as an example. A duct removes gas at the upper part of the furnace and a ventilator circulates the gases from the upper part of the furnace to the base of the furnace, a part of the gases removed at the upper part being evacuated to the exterior.
In an intermediate zone between the upper and lower parts of the furnace, air is injected into the furnace.
There is a partial combustion of the gases and carbon in the intermediate zone. The gases of combustion pass through the column of carbon above the intermediate zone exchanging their heat with that carbon and coming to a slightly elevated temperature in the upper part of the furnace. They are injected into the base of the furnace at slightly elevated temperature.
During ascent in the lower part of the furnace the gases are heated while cooling the solid materials through which the pass.
This known type of furnace is used to coke carbon to manufacture a combustible gas from carbon to fabricate coked pellets from carbon or a mixture of carbon and oxygen for use in a blast furnace and the like.